Formula for Alert or Message

Hi all,

First of all thanks for your help every time during our work if wee felt..

I have to prepare invoices daily basis..i have to write name in attached sheet i.e cell D7 and Operator name in G13..some time my boss catch my mistake that this operator is for any other company and some time he catchs that this company is for any other operator..

I have a list as there..kindly advise me if my operator is not equal to my company or my company is not equal to my operator as per my list in sheet 1 than a alert massenge should come there so that i would not continue typing till i correct it..

Is there any validation formula or any other advise..

Thanks in acvance for help

Attachment 59782